What means should be preferred to protect risky cross-connections?
There are several ways to protect risky cross-connections against backflow in a drinking water distribution system: the air gap, the barometric loop and the backflow prevention devices are the best known.
1. Air gap
The air gap requires cutting the piping, so it is not always possible to integrate it in practice. It consists of preventing any contact between the drinking water and the source of contamination. It is for this reason that it is necessary to avoid leaving a garden hose in the pool or in the garage sump. However, in institutional, commercial, and industrial settings, it is common for a hose to be connected to a tap and immersed in a boiler or basin containing toxic products or a detergent dispenser. The hose thus becomes a potentially risky cross-connection. The following figure, from B64.10-17, illustrates the proper use of air gap:
Figure 1 : Coupure antiretour (tirée de la norme CSA B64.10-17/B64.10.1-17)
2. Barometric loop
A second approach is to install a barometric loop. This is based on the theory that an atmospheric vacuum can lift water up to a height of 10 m. For this reason, the barometric loop should rise 10.7 m or more above the drinking water supply pipe. This method is effective in case of siphoning only and is mainly used in agriculture.
Figure 2 : Colonne barométrique (tirée de la norme CSA B64.10-17/B64.10.1-17)
3. Backflow prevention device
The other solution, which is more practical and suitable for many situations, is the installation of backflow prevention devices at strategic locations on the drinking water supply network. It is a mechanical device that prevents the spread of potentially contaminated water. There is a very wide variety of backflow prevention devices. Some must be inspected annually to ensure their proper functioning. For more information, see our blog post on the selection of a backflow prevention device.
